In fact, the whole offensive has bipartisan support. So it’s fair to say that there are very few within the government (including the opposition party of ‘no’) who do not support the action. The major reason for this offensive is that Gaddafi did not heed to the demands of the international community which were [source]:
Gadhafi must stop his troops from advancing on Benghazi, pull them back from Ajdabiya, Misurata, and Zawiyah, and establish water, electricity and gas supplies to all areas. Humanitarian assistance must be allowed to reach the people of Libya. Let me be clear, these terms are not negotiable.
The fear is that if the unrest in Libya is left unchecked, then the entire nation will descend into a civil war and there will be human-rights violation which is something the US is very protective of. Interestingly, doesn’t that argument make a stronger case for intervention in Darfur, Sudan? Of course it does! Then I wonder why the US refuses to intervene in what is arguably the worst abuses of human rights since Pol Pot’s regime.
We all know what’s going on. Libya has oil and Gaddafi is not a US puppet. Currently Gaddafi is struggling to maintain complete control over Libya. So US has both the motive and the opportunity to change the status quo. To place a figurehead in an oil-rich country so as to serve US interests. Lately, the US is being increasingly candid about its intentions. I suppose it is a good thing in some ways. For example, the US intentions are now common knowledge, instead of being mutual knowledge.
The most blatant admission of America’s abandonment a moral compass came from the Chairman of the Joint Chiefs of Staff Admiral Mullen. Given that the rulers in Bahrain and Yemen have used force against anti-government demonstrators, and yet, the US has intervened only Libya and not Bahrain or Yemen, Admiral Mullen argued [source]:
“We haven’t had a relationship with Libya for a long, long time. The Bahrainis and that country has been a critical ally for decades. So we’re working very hard to support a peaceful resolution there, as tragic as it has been, and we certainly decry the violence which has occurred in Bahrain. I just think the approach there needs to be different”
Translation: We don’t like Gaddafi, and so it’s ok to attack Libya under this pretext. We like the rulers of Bahrain and Yemen. They serve US interests. So we don’t care enough to ensure that the citizens of those countries actually enjoy any of the freedoms that we constantly exalt. All that matters is that US is better off in the end. Everything else is just a puppet show anyway.